1. Field of the Invention
The present invention relates to a data transfer method and a communication apparatus that uses the data transfer method to control data traffic transmitted across a network.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional router.
As shown in FIG. 1, in the conventional router 10, a LAN frame receiver unit (LFR) 12 receives a LAN frame from the network, and passes the received LAN frame on to a routing unit (RT) 14. The routing unit 14 performs the routing of the received LAN frame and passes it on to a LAN frame transmitter unit (LFT) 16. The LFT 16 transmits the LAN frame to the intended destination via the network.
FIG. 2 is a diagram for explaining a transfer of multiple mails across a network using a conventional mail transfer method, the mails including identical messages and different destinations. FIG. 3 is a sequence diagram for explaining a communication sequence when the mail transfer is performed as shown in FIG. 2.
Suppose that, in the mail transfer of FIG. 2, a mail server S1 is the source that sends three mails to the IP (Internet Protocol) network, and mail servers S2, S3 and S4 are the respective destinations that receive the mails from the IP network. One of the mails (indicated by “MAIL-S2” in FIG. 3) is sent from S1 to S2, the second (indicated by “MAIL-S3” in FIG. 3) is sent from S1 to S3, and the last (indicated by “MAIL-S4” in FIG. 3) is sent from S1 to S4. The mails include identical messages (frame#n) and different destinations (S2, S3, S4). The mails are transmitted at the same time through a number of routers R1, R2, R3, R4 and R5 in the network to the respective destinations.
As shown in FIG. 2 and FIG. 3, when transmitting the mails from the server S1 to the servers S2, S3 and S4 included in the mailing list by using the conventional mail transfer method, the mails including the identical messages are simultaneously transferred from the server S1 to the servers S2, S3 and S4, independently. In the conventional routers, such as the routers R1 through R5, mail frames are routed in the same manner as other data frames, and a special recognition of mail frames is not performed. The respective mail frames are merely routed to the next-node equipment of the network by the conventional routers. Specifically, in the mail transfer of FIG. 2, the routing of a mail containing identical messages is repeated by the number of the corresponding mails between the router R1 and the router R2 and between the router R2 and the router R4.
The conventional routers are not provided with a mechanism for recognizing that multiple mail frames, including identical messages and different destinations, are transferred across the network from the source server to the destination servers. The respective mail frames, delivered from the source server, are merely routed to the next-node equipment of the network by the conventional routers. For this reason, when mail traffic on the transmission lines of the conventional routers is expected to increase, it is necessary to add additional transmission lines to the existing transmission lines of the conventional routers. There has been no other countermeasure that can be taken with the conventional routers.
In a case of mail traffic in local areas covered by one domain, such as cooperate LAN or Internet service provider (ISP) networks, the implementation of distributed mail servers can be the countermeasure for reduction of the increasing mail traffic.
However, in a case of mail traffic in the worldwide network spanning multiple domains, when a plurality of mail frames including identical messages and different destinations are transferred across such network from the source server to the destination servers, the load of mail traffic on the transmission lines where many domains are concentrated becomes heavy. Further, when transmitting mails with a large attachment file across such network, the load of mail traffic on the network resources becomes very heavy. The larger the number of mail servers installed, the heavier the load of mail traffic in the network. The larger the size of a mail frame transmitted across the network, the heavier the load of mail traffic in the network.
In recent years, with the proliferation of the Internet, the mail traffic, such as mailing list or e-mails with multiple destinations, has rapidly grown, which is liable to narrowing the band available to the routing lines in the network. There is an increasing demand for providing an effective mechanism for reduction of the increasing mail traffic in the worldwide network spanning multiple domains.